The Crown Victoria is the most popular police car in the country, "but every year there are a couple of police (car) explosions involving the Crown Vic," said Clarence Ditlow, president of the Center for Auto Safety, a Washington, D.C., group focused on the U.S. automotive industry which has unsuccessfully tried to get the Crown Victoria recalled after the fiery deaths and injuries of dozens of law enforcement officers around the country.

"You have officers who survive the trauma of a crash, but they die by fire and that should never happen," Ditlow said.

Police Maj. Kurt Kendro acknowledged Monday that an unspecified number of rounds of ammunition ignited inside Davis' car after it was rear-ended Saturday night while Davis was trying to help motorists whose car broke down on the H-1 freeway.

"I can confirm that rounds did explode," Kendro said.

He declined to provide additional details, saying the case remains under investigation.

Davis had moved to Hawaii from California to join the police force and graduated from the 161st recruit class in 2008, spokeswoman Caroline Sluyter said.

He was driving paperwork from the Wahiawa substation to the police headquarters when he stopped his car behind a black Chevrolet pickup truck that was stalled in the left eastbound lane of the H-1 at the Kaonohi Street overpass in Aiea.

Davis had turned on the blue police lights on the Crown Victoria but had not gotten out of the car when it was struck from the back by a Chevrolet Silverado driven by a 41-year-old man who was later arrested on suspicion of negligent homicide, Police Chief Louis Kealoha said Sunday.

Davis' older sister, Amanda Stevens of California, said, "My brother would want us to forgive the driver that hit him."

Funeral services for Davis are tentatively scheduled for Feb. 7 in Honolulu, Stevens said. Another service will be held in California later, she said.

Sluyter said police officials have no comment on the safety record of the Ford Crown Victoria Police Interceptor.

The city Medical Examiner's Office on Monday said it is not releasing the cause of death.

Traffic investigators were still seeking witnesses Monday and urged people to call investigators at 529-3499.

By some estimates, 75 percent of America's law enforcement departments use the Crown Victoria model. But its dominance wasn't intentional, Ditlow said.

"Both Chrysler and GM got out of the full-size, police fleet market," he said. "The Crown Vic won by default."

In 2002 the Center for Auto Safety unsuccessfully asked Ford and the National Highway Traffic Safety Administration to recall the vehicle, but efforts instead were made to retrofit them to help protect fuel tanks and outfit them with fuel-suppression systems, Ditlow said.

State troopers, police officers, sheriff's deputies and other law enforcement officers continued to die in fiery crashes of the model.

From 1994 to 2009 the Crown Victoria was involved in 135 fatal law enforcement-related collisions around the country, according to the center.

Fire was a factor in 38 of the crashes, and 186 people died in collisions that involved the Crown Victoria.

"The Crown Vic is a safe vehicle other than its fuel tank, which is located behind the rear axle in the so-called 'crush zone' of a rear impact," Ditlow said. "The Crown Victoria is nothing more than an overgrown (Ford) Pinto."

Officers love the Crown Victoria's large trunk room for all of their equipment, its rear-wheel drive and roomy interior, Ditlow said.

"It is a good vehicle, but it has a terrible fuel system," he said.

Davis, 28, graduated from Folsom High School in Northern California in 2001, his sister said.

He was a member of the track and field team and played saxophone in the marching band.

In 2005 Davis graduated from San Francisco State University, where he was a member of the Pi Kappa Phi fraternity.

Davis is survived by his mother, Rhonda; a daughter, Mackenzie Rose, age 3; his sister; and a niece, Hailey.

Davis' death follows the Sept. 13 death of Officer Eric Fontes, who was struck and killed along Farrington Highway near Ko Olina while helping fellow officer Herman "Sam" Scanlan during a traffic stop.

Fontes, 45, died when he was struck by a pickup truck. Scanlan was injured when the pickup then hit a Dodge Durango that crashed into him.

Maj. Kendro on Monday urged legislators to pass House Bill 2070, one of five bills introduced that would make Hawaii the last state to require motorists to move over at least one lane and get out of the lane that contains police, fire, ambulance and other emergency vehicles.

"That gives the first responder -- whether police, fire, EMS, lifeguards, tow trucks, maybe even the state Freeway Service Patrol -- to operate and do whatever they need to get done for the safety of the person responding as well as the motorist," Kendro said.

Drivers also would be required to slow down to 25 mph on a highway or 20 mph in a residential area.

"Hawaii boldly stands out as the only state that does not have this law," Kendro said.

Davis' sister, also pleaded with lawmakers to pass such a bill.

"We beg the Legislature to pass a law that motorists should pull over when they see police lights," she said. "Tell that driver (who hit Davis) to make it his life's work to make sure that law is passed and to make sure no one else makes the same mistake that killed my brother or kills another officer."

Hawaii News Now video: Push for 'move over' legislation after death of HPD officer